1. Field of the Invention
This invention relates to the gasification of carbonaceous materials. More particularly, the invention relates to the conversion of a solid carbonaceous fuel into gaseous products having increased fuel valued and ease of capture of carbon dioxide by-products.
2. Description of the Prior Art
Gasification has been used since the early 1800's to produce town gas from coal. Town gas was the most important gaseous fuel during the early industrial revolution and was used mainly for lighting, heating, and cooking. Starting around 1900, gasification was used to produce fuel with equal parts of hydrogen and carbon monoxide. Now, gasification processes can convert coal or coke into syngas, which can be used to produce electricity in an integrated gasification combined cycle (IGCC) process or as a starting point in many chemical processes.
Gasification reactors can convert generally solid feedstocks into gaseous products. For example, gasification reactors can gasify carbonaceous feedstocks, such as coal and/or petroleum coke, to produce desirable gaseous products such as hydrogen. Gasification reactors must be constructed to withstand the significant pressures and temperatures required to gasify solid feedstocks.
Generally, carbon in the coal or coke can be converted into gas by partial combustion with oxygen, according to the following equations.C+O2→CO2 and C+½O2→COCarbon also can react with water in an endothermic water gas reaction.C+H2O→CO+H2 The shift reaction can convert all or part of the carbon monoxide into hydrogen to reach equilibrium.CO+H2OCO2+H2 The final mixture which comprises hydrogen and carbon monoxide is called syngas.
In some applications, gasification can occur in the presence of air, which contains nitrogen, and gasification reactors can create by-products that need to be treated or disposed of due to environmental concerns. Thus, during the combustion process, carbon dioxide and nitrogen-containing compounds, such as oxides of nitrogen and amines, can be formed. Environmental regulations more frequently require the collection and sequestration of carbon dioxide. Amine separator units which are necessary to remove acidic compounds, such as, for example, H2S and CO2, are very energy intensive, are large and thus have a massive footprint, and can be very costly to operate and maintain.
Some gasification processes can use only one oxy-fired reactor, but incomplete combustion results in an inefficient process with sub-standard energy and/or product output.